A known example of shim of the above-specified type is shown in FIG. 1. The shim 10 comprises two branches 14 and a base 12 interconnecting the two branches 14. It also comprises at one of its ends 10a, a holder tongue 16. The holder tongue 16 projects from the edge 12a of the base 12 and is folded to extend between the branches 14.
FIG. 2 is a fragmentary exploded view showing a known rotor assembly 20 forming part of a fan module of an airplane turbojet. The assembly 20 comprises a rotor disk 21 presenting recesses or slots 22 in its outer periphery, and for each recess 22: a blade 25 fastened via its root 26 in the recess 22; a shim 10 of the kind shown in FIG. 1; a spacer 28; and a latch 30. The rotor assembly 20 is shown in the assembled state in FIG. 3.
To assemble the assembly 20, the shim 10 is initially mounted on the blade root 26, being slipped thereon from the upstream side of the blade, along arrow F (see FIG. 2). The shim 10 thus surrounds the blade root 26, with the branches 14 of the shim respectively covering the bearing surfaces 26a of the blade root. The bearing surfaces 26a of the blade root 26 and the bearing surfaces 22a of the recesses 22 are those surfaces of the blade roots 26 and of the recesses 22 (i.e. of the disk 21) that come into abutment against one another under the effect of centrifugal forces during rotation of the assembly 20.
Thereafter, the blade root 26 carrying the shim 10 is slotted into a recess 22. On its downstream side, the blade 25 comes into abutment against a wall 27 of the drum of the low-pressure compressor of the turbojet (see FIG. 3).
The latch 30 is then put into position in front of the blade root 26 against the holder tongue 16 of the shim 10.
Finally, the spacer 28 is slid between the shim 10 and the bottom 22b of the recess 22. The latch 30 is then held between the upstream rim 28a of the spacer 28 and the blade root 26 in such a manner that the holder tongue 16 is held between the latch 30 and the blade root 26, thus preventing any axial movement of the shim 10 relative to the blade root 26.
The shim 10 is an intermediate part between the blade 25 and the rotor disk 21. It forms a kind of sock covering the root 26 of the blade 25 and it serves to fill in the clearance between the blade root 26 and the disk rotor 21. This clearance can exist from the beginning (i.e. from the design of the blade 25 and the disk 21), however it is mostly the result of the disk 21 being mechanically reworked during repair.
The following drawback often occurs with the prior art shim 10: because of its shape and its elasticity, it can happen that the shim 10 is erroneously mounted back to front, i.e. that it is engaged from the rear (i.e. the downstream end) of the blade 25 instead of being engaged from the front (i.e. the upstream end) thereof. Under such circumstances, the holder tongue 16 is situated downstream from the blade root 26 and is not held between the latch 30 and the blade root. The shim 10 is then not retained by the holder tongue 16 and can move axially. This back-to-front mounting of the shim 10 leads to the disk 21 being damaged due to the shim 10 bearing badly against the disk (more precisely due to the reduction in the contact areas between the shim and the disk), thereby making it necessary in the long run to replace the disk 21.